U.S. patent number 7,074,336 [Application Number 09/886,175] was granted by the patent office on 2006-07-11 for inorganic ion sorbents and methods for using the same.
This patent grant is currently assigned to Sandia Corporation. Invention is credited to Patrick V. Brady, James L. Krumhansl, David M. Teter.
United States Patent |
7,074,336 |
Teter , et al. |
July 11, 2006 |
Inorganic ion sorbents and methods for using the same
Abstract
A process and medium for decontamination of water containing
anionic species including arsenic and chromium, wherein compounds
comprising divalent and trivalent metal oxides and sulfides are
used to form surface complexes with contaminants under pH
conditions within the range of potable water. In one embodiment
natural and synthetic spinels and spinel-like materials are used as
the sorbent substance.
Inventors: |
Teter; David M. (Edgewood,
NM), Brady; Patrick V. (Albuquerque, NM), Krumhansl;
James L. (Albuquerque, NM) |
Assignee: |
Sandia Corporation
(Albuquerque, NM)
|
Family
ID: |
36644032 |
Appl.
No.: |
09/886,175 |
Filed: |
June 20, 2001 |
Current U.S.
Class: |
210/683; 210/911;
210/913; 210/684 |
Current CPC
Class: |
B01J
20/08 (20130101); B01J 20/0237 (20130101); C02F
1/281 (20130101); B01J 20/06 (20130101); B01J
20/0229 (20130101); Y02C 10/08 (20130101); C02F
2101/22 (20130101); C02F 1/683 (20130101); Y10S
210/911 (20130101); Y02C 20/40 (20200801); C02F
2101/103 (20130101); Y10S 210/913 (20130101) |
Current International
Class: |
C02F
1/28 (20060101) |
Field of
Search: |
;210/683,684,911,913 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
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Iron Hydroxide," Water Research, vol. 16, 1982, 1247-1253. cited by
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of As(V) on Geologic Materials," Water, Air, and Soil Pollution 40
(1988) 293-305. cited by other .
Benjamin et al., "Sorption and Filtration of Metals Using
Iron-Oxide-Coated Sand," Water Research, vol. 30, No. 11, 1996,
2609-2620. cited by other .
Singh et al., "Adsorption technique for the treatment of As(V)-Rich
Effluents," Colloids and Surfaces A: Physicochemical and
Engineering Aspects, 111, 1996, 49-56. cited by other .
Matis et al., "Flotation Removal of As(V) onto Goethite,"
Environmental Pollution, vol. 97, No. 3, 1997, 239-245. cited by
other .
Driehaus et al., "Granular Ferric Hydroxide--A New Adsorbent for
the Removeal of Arsenic from Natural Water," J. Water SRT--Aqua,
47, 1998, 30-35. cited by other .
Balsley et al., "Anion Scavengers for Low-Level Radioactive Waste
Repository Backfills," Journal of Soil Contamination, 7(2), 1998,
125-141. cited by other .
Viravarghavan et al., "Arsenic in Drinking Water--Problems and
Solutions," Water Science & Technology, vol. 40, No. 2, 1999,
69-76. cited by other .
Fryxell et al., "Design and Synthesis of Selective Mesoporous Anion
Traps," Chemistry of Materials, vol. 11, No. 8, 1999, 2148-2154.
cited by other .
Lefevre et al., "Uptake of lodide by a Mixture of Metallic Copper
and Cupric Compounds," Environmental Science & Technology, vol.
33, No. 10, 1999, 1732-1737. cited by other .
Lefevre et al., "Sorption of lodide on Cuprite (Cu.sub.20),"
Langmuir, vol. 16, No. 10, 2000, 4519-4527. cited by other .
Wu et al., "Competitive Adsorption of Molybdate, Chromate, Sulfate,
Selenate, and Selenite on .gamma.-Al.sub.2O.sub.3," Colloids and
Surfaces A: Physicochemical and Engineering Aspects, 166, 2000,
251-259. cited by other .
Chiu et al., "Arsenic Adsorption and Oxidation at Manganite
Surfaces. 1. Method for Simultaneous Determination of Adsorbed and
Dissolved Arensic Species," Environmental Science & Technology,
vol. 34, No. 10, 2000, 2029-2034. cited by other.
|
Primary Examiner: Cintins; Ivars C.
Attorney, Agent or Firm: Elliott; Russell D. Vilven-Doggett;
Janeen
Government Interests
This invention was made with support from the United States
Government under Contract DE-AC04-96AL85000 awarded by the U.S.
Department of Energy. The Government has certain rights in this
invention.
Claims
We claim:
1. A process for decontaminating water, comprising: selecting a
sorbent material that binds anionic species predominantly through
the formation of surface complexes, said sorbent material
comprising a composition including formula (AB.sub.2X.sub.4).sub.n
wherein A is a divalent cation, B is a trivalent cation, X is an
anion species and n is at least one, wherein, said selected sorbent
material is CuFe.sub.2O.sub.4; and decontaminating water by
contacting said selected sorbent material with water containing
anionic contaminants selected from the group consisting of species
including chromium and species including arsenic, said
decontaminating substantially removing the anionic contaminants.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to decontamination of fluids containing
ionic contaminants, especially water containing anionic
contaminants. In particular, the invention relates to the removal
of arsenic contaminants and chromate from water by treating the
water using adsorbent compounds comprised of divalent and trivalent
metal oxides and sulfides.
2. Description of the Related Art
For purposes of this disclosure, unless otherwise specified, the
term "metal oxides" is intended to include both metal oxides and
metal hydroxides. Likewise, the term "metal sufides" is intended to
include both metal sulfides and metal hydrosulfides. Similarly, for
purposes of this disclosure, "arsenic contaminants" includes both
arsenates and arsenites.
Arsenic contaminants are examples of anionic contaminants that may
be present in water as a result of natural as well as
human-mediated causes. The long-term availability of safe and
affordable drinking water depends, in part, on availability of
effective and economical treatment means for removing arsenic
contaminants (as well as other anionic contaminants including
chromate) from water. Successful treatment strategies, in turn,
depend on not otherwise significantly altering the water
characteristics (for example, its pH) in ways that would make it
non-potable.
Arsenic and other anionic contaminants likewise pose risks when
present in fluids other than drinking water sources. For example,
waste water streams often contain such contaminants and require
remediation even where they are not considered to be directly
associated with potable drinking water sources.
Various sorbent methods for removing arsenic contaminants and other
anionic contaminants from water have been used and developed
previously. For example, certain trivalent metal hydroxide
compounds, such as Al.sub.2O.sub.3 and Fe.sub.2O.sub.3, have been
demonstrated to sorb anionic contaminants, including arsenic
contaminants, from water. A drawback associated with use of such
trivalent compounds alone is that, because they typically exhibit a
point of zero charge from pH 7 to 9, the water to be treated may
need to be acidified in order for these compounds to sorb anions to
a significant degree. Thus, after treatment, in order to restore
the potability of the treated water, further amendments must be
added to bring the pH back up to a safely drinkable range.
Similarly, tetravalent metal oxides such as SiO.sub.2 could be
effective anion sorbents, however, their point of zero charge is
typically around pH 2, so extremely acidic conditions would needed
for tetravalent metal oxides to sorb anions. Additionally, these
substances are considered likely to fall outside of the range of
useful sorbents because of other chemical issues associated with
operating at such low pH.
The divalent oxide MgO, likewise, has been shown chemically to sorb
anions including arsenic in water. Although use of MgO does not
necessitate driving the pH of water outside of the potable range
(divalent metal oxides tend to exhibit a point of zero charge that
is pH 10 or higher), the effectiveness of MgO as a sorbent for
water decontamination, however, can be limited. This is due to its
tendency to form carbonates in the presence of carbon in the water
from natural (e.g. biological and atmospheric) sources. When this
occurs, the carbonate species formed at the surface lack any
significant electrostatic attraction for negatively-charged ions.
Thus, the sorbency of the MgO can be short-lived absent taking
steps to reverse of the carbonate reaction and restore the
sorbent.
The sorbency methods just discussed rely on the electrostatic
attraction between positively charged surface species and
negatively charged contaminants. An altogether different mechanism
that has been exploited to decontaminate water containing ionic
contaminant species is ion exchange. Examples of ion exchange
materials suitable for water decontamination include hydrotalcites
(which exchange anions) and zeolites (which exchange cations).
Although ion exchange materials have been shown to be effective
without causing the types of problems associated with Fe(OH).sub.3
and Al.sub.2O.sub.3 (pH concerns) or MgO (carbonate issues), ion
exchange materials can be very expensive. Zeolites that allow for
separations based on size are also used in some decontamination
applications, but they do not sorb anionic species such as chromate
and arsenic contaminants in water.
Therefore, the need remains for improved liquid decontamination
approaches that are inexpensive, yet effective in removing anionic
contaminants, including chromate, arsenates and arsenites.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a water decontamination
process comprising contacting water containing anionic contaminants
with sorbent material that binds anionic species predominantly
through the formation of surface complexes, wherein the sorbent
material comprises divalent metals and trivalent metals.
In another aspect, the invention provides a decontamination medium
for water comprising sorbent material that binds anionic species
predominantly through the formation of surface complexes, wherein
the sorbent material comprises divalent metals and trivalent
metals.
DETAILED DESCRIPTION OF THE INVENTION
This invention utilizes the principle that metal oxides and metal
sufides, at pH below their point of zero charge, attract negatively
charged species. This is due to a phenomenon wherein, at pH below
the point of zero charge for a given metal oxide or metal sufide,
surface metal groups tend to be more fully protonated (and thus
more likely to exhibit a positive charge) than at pH at or above
the point of zero charge. As a result, at pH below the point of
zero charge, negatively-charged species can be removed from
solution through the formation of ion-bearing surface complexes
with the metal oxide or metal sulfide surface groups.
The mixed divalent and trivalent metal oxide and metal sulfide
materials employed in the present invention to adsorb
negatively-charged contaminant species in water do so at pH within
the drinkable range for water. Moreover, the materials tested do
not exhibit the tendency to form carbonates to a degree sufficient
to render them inactive for purposes of anion sorption. According
to the invention, sorbent materials effective for sequestering
arsenic-containing contaminants from water are selected, or can be
engineered, to exhibit a point of zero charge that permits anion
sorption in the pH range of potable water.
An example of mixed valency inorganic materials capable of sorbing
anions such as arsenic contaminants and chromate in water is found
in natural and synthetic spinels and inverse spinels, as well as
"spinel-like" materials. These inorganic materials are generally
characterized by the chemical formula (AB.sub.2X.sub.4).sub.n where
A and B represent cations of differing valencies (such as
A=Mg.sup.2+ and B=Al.sup.3+) and X represents one or more anions
(such as O.sup.2- or S.sup.2-) and n is at least 1. (For purposes
of this disclosure, these stoichiometries are intended to be
approximate so that where the formula (AB.sub.2X.sub.4).sub.n is
used in this disclosure, this means that B has a prevalence of
about twice that of A and X has a prevalence of about four times
that of A. Also, in this disclosure, "spinel-like" is intended to
encompass substances generally exhibiting the stoichiometry just
noted, but which tend to be poorly crystalized. "Spinel-like"
includes structures tend to approximate the spinel structure and
also generally exhibit x-ray diffraction patterns typical of
natural or synthetic spinels).
Examples of natural spinels suited for application according to the
invention include MgAl.sub.2O.sub.4 (Spinel), MnAl.sub.2O.sub.4
(Galaxite), FeAl.sub.2O.sub.4 (Hercynite), ZnAl.sub.2O.sub.4
(Gahnite), MgFe.sub.2O.sub.4 (Magnesioferrite), MnFe.sub.2O.sub.4
(Jacobsite), Fe.sub.3O.sub.4 (Magnetite), ZnFe.sub.2O.sub.4
(Franklinite), NiFe.sub.2O.sub.4 (Trevorite), CuFe.sub.2O.sub.4
(Cuprospinel), Fe.sub.3S.sub.4 (Greigite), MgCr.sub.2O.sub.4
(Magnesiochromite), (Mn,Fe)(Cr,V).sub.2O.sub.4 (Manganochromite),
FeCr.sub.2O.sub.4 (Chromite), (Ni,Fe)(Cr,V).sub.2O.sub.4
(Nichromite), (Co,Ni)(Cr,Al).sub.2O.sub.4 (Cochromite),
MgV.sub.2O.sub.4 (Magnesiocoulsonite), FeV.sub.2O.sub.4
(Coulsonite), (Mn,Fe)(V,Cr).sub.2O.sub.4 (Vuorelainenite),
Mn.sub.3O.sub.4 (Hausmannite), CuCO.sub.2S.sub.4 (Carrolite),
CuBi.sub.2O.sub.4 (Kusachiite), Mn(Mn,Fe).sub.2O.sub.4 (Iwakiite)
and ZnMn.sub.2O.sub.4 (Hataerolite).
The sorbent material comprises a chemical substance selected from
the group consisting of a first composition in which a species A
has a prevalence of about half that of a species B, and a species X
has a prevalence of about four times that of the species A wherein
for either composition A and B are metal species and X is selected
from the group consisting of oxygen and sulfur. The sorbent
material comprises a chemical substance having the first
composition, and A is selected from the group consisting of
Co.sup.2+, Cu.sup.2+, Fe.sup.2+, Mg.sup.2+, Mn.sup.2+, Ni.sup.2+,
Zn.sup.2+, and combinations thereof, and B is selected from the
group consisting of Al.sup.3+, Bi.sup.3+, Co.sup.3+, Cr.sup.3+,
Fe.sup.3+, Mn.sup.3+, Ni.sup.3+, V.sup.3+ and combinations
thereof.
For purposes of this invention, compounds having generally the
AB.sub.2X.sub.4 formula A can include any of the following:
Co.sup.2+, Cu.sup.2+, Fe.sup.2+, Mg.sup.2+, Mn.sup.2+, Ni.sup.2+
and Zn.sup.2+, and B can include any of the following: Al.sup.3+,
Bi.sup.3+, Co.sup.3+, Cr.sup.3+, Fe.sup.3+, Mn.sup.3+ and
V.sup.3+.
In demonstrating the present invention, it has been shown that
adsorption of arsenic contaminants by mixed valency inorganic
materials occurs largely independently of their degree of
crystallization. For purposes of the present invention, it is
recognized that the degree of crystallinity of, for example, spinel
and spinel-like materials can vary from a slightly disordered
amorphous material to a highly ordered material characterized by
the face-centered cubic structures typically associated with
natural spinels. This variability in crystallinity depends on
factors such as particle size, exposure to heat, and time. Yet,
according to the invention, so long as metal oxide and/or metal
sufide groups in a protonated state are in contact with the liquid
containing the anionic contaminants, those anionic species can be
successfully sorbed.
At any given pH, the extent of sorption is measured in terms of
K.sub.d (ml/g). This value represents the sorption coefficient,
that is, the ratio of contaminant sorbed (moles/g) to contaminant
in solution (moles/ml):
Kd(ml/g)=[(Co--Ce)/Ce].times.[Vsol(cc)/Mads(g)] where Co represents
initial concentration, Ce represents final concentration, Vsol
represents total volume of solution, and Mads represents total mass
of adsorbent. Materials with Kd values greater than 100 ml/g are
generally considered strong candidates for use as contaminant
sorbents.
Without further elaboration, it is believed that one skilled in the
art can, using the preceding description, utilize the present
invention to its fullest extent. The following example of an
embodiment is therefore intended to be construed as merely
illustrative and not limitative of the remainder of the disclosure
in any way whatsoever.
EXAMPLE
The following is an example showing synthesis, characterization and
testing of MgAl.sub.2O.sub.4 for purposes of decontamination of
arsenic-containing aqueous solutions.
Synthesis and Characterization: A 500 ml solution of 0.14M
Mg(NO.sub.3).sub.2.6H.sub.2O (reagent grade) in deionized water was
combined with a 500 ml solution of Al(NO.sub.3).sub.3.9H.sub.2O
(reagent grade) in deionized water and mixed thoroughly using a
magnetic stirrer. A solution of 3M NaOH (reagent grade) was added
dropwise until the mixture reached a pH of approximately 9.0, at
which point the Mg.sup.+2 and Al.sup.+3 precipitated out of
solution as mixed hydroxides. These precipitates were allowed to
age for 24 hours at 298K, and were then centrifuged and washed
multiple times with deionized water to remove all NaNO.sub.3 salts.
The precipitates were then filtered with a Millipore pneumatic
filter apparatus using a 0.45 .mu.M filter and then mixed with 500
ml of pure ethanol (reagent grade). The resulting slurry was then
allowed to dry in trays at ambient temperature and humidity. These
powders were then divided into three groups (unheated), heated for
4 hours at 673K in an oxidizing atmosphere, and heated for 4 hours
at 1073K in an oxidizing atmosphere. These powders were then
characterized using X-ray diffraction. The results of these
analyses are included in Table 1.
Testing: Batch sorption experiments were then performed to test the
ability of MgAl.sub.2O.sub.4 to sorb arsenate (AsV) and chromate
(Cr6). Solutions containing 100 ppb, 1 ppm, and 100 ppm of arsenate
(or chromate) in a tap water matrix were synthesized. The analysis
of the tap water is given in Table 2. In these experiments, 0.25 g
of the unheated and heat-treated sorbents were mixed with 20 ml of
the arsenic containing solutions for a contact time of 5 minutes.
The solutions were then filtered using a 0.2 um filter and the
resulting arsenic concentration was analized using inductively
coupled plasma mass spectroscopy (ICP-MS). The results of these
analysis and the calculated Kd's are presented in Table 3.
Similar synthesis was performed for a number of other compounds.
Table 1 presents x-ray diffraction results showing phases resulting
for various stoichiometries at different temperatures. Table 2
presents an analysis of the tap water matrix used prior to adding
arsenic. This is instructive since it demonstrates, in conjunction
with Table 3, that parts per billion levels of arsenic can be
removed from water using the invention even where parts per million
levels of other naturally occurring substances are present in the
water. Table 3 presents sorption results for both arsenic and
chromate.
TABLE-US-00001 TABLE 1 Unheated (298.degree. C.) 400.degree. C.
800.degree. C. CoAl.sub.2O.sub.4 Al(OH).sub.3 + CoOOH
CoAl.sub.2O.sub.4 (spinel) CoAl.sub.2O.sub.4 (spinel)
CuAl.sub.2O.sub.4 CuAl.sub.2O.sub.4 (spinel-like) + CuO
CuAl.sub.2O.sub.4 (spinel-like) + CuO CuAl.sub.2O.sub.4 (spinel)
MgAl.sub.2O.sub.4 Al(OH).sub.3 + Mg(OH).sub.2 MgAl.sub.2O.sub.4
(spinel-like) MgAl.sub.2O.sub.4 (spinel) NiAl.sub.2O.sub.4
Al(OH).sub.3 + NiOOH NiAl.sub.2O.sub.4 (spinel-like)
NiAl.sub.2O.sub.4 (spinel) ZnAl.sub.2O.sub.4
Zn.sub.6Al.sub.2(OH).sub.16CO.sub.34H.sub.2O + Al(OH).sub.3
ZnAl.sub.2O.sub.4 (spinel-like) ZnAl.sub.2O.sub.4 (spinel)
CuCr.sub.2O.sub.4 Cu.sub.3CrO.sub.6.2H.sub.2O + Cr(OH).sub.3
CuCr.sub.2O.sub.4 (spinel-like) + Cr.sub.2O.sub.3 CuCr.sub.2O.sub.4
(spinel-like) + Cr.sub.2O.sub.3 CuFe.sub.2O.sub.4 CuFe.sub.2O.sub.4
(spinel-like) CuFe.sub.2O.sub.4 (spinel) + CuO + Fe.sub.2O.sub.3
CuFe.sub.2O.sub.4 (spinel) MgFe.sub.2O.sub.4 MgFe.sub.2O.sub.4
(spinel-like) MgFe.sub.2O.sub.4 spinel) MgFe.sub.2O.sub.4 (spinel)
ZnFe.sub.2O.sub.4 ZnFe.sub.2O.sub.4 (spinel-iike) ZnFe.sub.2O.sub.4
(spinel) ZnFe.sub.2O.sub.4 (spinel)
TABLE-US-00002 TABLE 2 (General Chemistry Analysis of Tap Water
Matrix) pH 7.7 Chloride 33 ppm Silica 40 ppm as SiO.sub.2 Sulfate
26 ppm Fluoride 1 ppm Bicarbonate 106 ppm as CaCO.sub.3
TABLE-US-00003 TABLE 3 ARSENIC SORPTION Arsenic Arsenic Init. Final
Conc Conc. Kd Material (ppb) (ppb) (ml/g) CoAl.sub.2O.sub.4
(spinel-800 C.) 132 2 5200 CuAl.sub.2O.sub.4 (spinel-like-400 C.)
132 <0.2 52720 CuAl.sub.2O.sub.4 (spinel-800 C.) 132 1.9 5478
MgAl.sub.2O.sub.4 (spinel-like-400 C.) 192 5 2992 MgAl.sub.2O.sub.4
(spinel-800 C.) 192 16 880 NiAl.sub.2O.sub.4 (spinel-like-400 C.)
132 <0.2 52720 NiAl.sub.2O.sub.4 (spinel-800 C.) 132 2.6 3982
ZnAl.sub.2O.sub.4 (spinel-like-400 C.) 132 <0.2 52720
ZnAl.sub.2O.sub.4 (spinel-800 C.) 132 0.7 15006 Co.sub.3O.sub.4
(spinel-400 C.) 132 4.5 2267 CuFe.sub.2O.sub.4
(spinel-like-unheated) 132 0.4 26320 CuFe.sub.2O.sub.4 (spinel-400
C.) 132 13 732 MgFe.sub.2O.sub.4 (spinel-like-unheated) 132 0.72
14587 MgFe.sub.2O.sub.4 (spinel-400 C.) 132 1.2 8720
ZnFe.sub.2O.sub.4 (spinel-like-unheated) 132 0.9 11653
ZnFe.sub.2O.sub.4 (spinel-400 C.) 132 6.7 1496 CHROMATE SORPTION Cr
Cr Init. Final Conc Conc. Kd Material (ppb) (ppb) (ml/g)
CoAl.sub.2O.sub.4 (spinel-800 C.) 1010 3 26853 CuAl.sub.2O.sub.4
(spinel-800 C.) 1010 81 916 MgAl.sub.2O.sub.4 (spinel-like-400 C.)
1010 122 582 NiAl.sub.2O.sub.4 (spinel-like-400 C.) 1010 3 26853
NiAl.sub.2O.sub.4 (spinel-800 C.) 1010 104 697 ZnAl.sub.2O.sub.4
(spinel-like-400 C.) 1010 3 26853 CuFe.sub.2O.sub.4
(spinel-like-unheated) 1010 40 1940 MgFe.sub.2O.sub.4
(spinel-like-unheated) 1010 39 1992 MgFe.sub.2O.sub.4 (spinel-400
C.) 1010 31 2526
From the foregoing description, one skilled in the art can easily
acertain the essential characteristics of the invention defined in
this specification and the appended claims, and without departing
from the spirit and scope thereof can make various changes and
modifications of the invention to adapt it to various usages and
conditions. Such changes and modifications as would be obvious to
one skilled in the art are intended to be included within the scope
of the following claims. Additional advantages and novel features
will become apparent to those skilled in the art upon examination
of the following description or may be learned by practice of the
invention.
* * * * *